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        // 字符串   带引号的都是字符串

        var a = 'hi';
        var b = '<div></div>';
        var c = '1';
        var d = 'true';
        var e = 'null';
        var f = 'undefined';
        var h = '';   // 空字符串不等同于null


        console.log(typeof h);
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